Hinge fittings for motor vehicle seats are parts which are manufactured on an industrial scale and in numbers of several million annually. Nowadays, the assembling, in this regard, is carried out fully automatically, comprising a screening inspection, and is continued round the clock, for an optimal utilization of the machines and assembling apparatus. Under these given circumstances, a high degree of reliability must be striven for from the outset when designing a hinge fitting, such that it is possible to carry out the assembly rapidly and, above all, fully automatically and trouble-free. This high degree of reliability may be ensured relatively readily by providing suitably large positive allowances for the assembly of the individual parts. In the case of a hinge fitting for motor vehicle seats, considerable limits are, however, imposed in this regard, since the sum total of all allowances makes itself felt as a certainly considerable and unpleasant backlash at the upper edge of the backrest. Since the requirement is to keep the play of the backrest as small as possible, the designer of the hinge fitting is thus obliged to aim for the narrowest tolerances possible. Thus, in conjunction with the dependability, which is referred to as operating reliability, in the automatic manufacture of parts on an industrial scale, this results in distinctly conflicting objectives.
In a hinge fitting of the kind which is presupposed as being known for example from DE 27 24 637, the mounting of the eccentric is statically overdesigned. The statically overdesigned mounting has the drawback that a satisfactory adjustment is possible only when the backrest fitting mounting plates, which are provided on different sides of the eccentric, are arranged such that the mounting bores are accurately aligned. In industrial scale manufacture, this requirement cannot be met to the desired extent. When there are alignment errors, the swivelling axis is out-of-true, resulting in a sluggish adjustment together with a considerable reduction in comfort. To give practical effect to this construction, it is necessary that the positive mounting allowances in the two mounting bores are designed to be correspondingly large. Although this ensures the desired smooth adjusting action, it does have the drawback that an undesirably large backrest backlash must set in.
In addition, a further hinge fitting of the kind is known (DE 32 26 714 C2), in which the eccentric is mounted in a statically defined manner. Only one bearing is provided per hinge member. Loading of the backrest tends to twist the two hinge members relative to each other. The resultant forces are transferred to the swivelling axis bearing regions via the bearings. This causes a moment which brings about an out-of-true position of the axis. This out-of-true position results in canting of the bearings and in a resultant stiff adjusting action. This problem is particularly serious when the bearings are formed by steel-on-steel bearings having a grease lubrication.
Starting out from the above-mentioned state of the art, the invention is based on the object of designing a hinge fitting of the kind presupposed as being known, such that the drawbacks of the known pertinent hinge fittings are avoided. It is intended to provide a hinge fitting which has a smooth action even when the tolerances in the bearings are kept relatively small. Besides, it should be possible to adhere, with a relatively low manufacturing outlay, to such very small bearing clearance tolerances and to achieve a high degree of process reliability in the manufacture of the individual members and in the assembly.